JPH11201841A - Pressure change measuring device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To exclude influences according to sudden change of temperature environment by an external flowing medium such as a sea bottom water stream or the like. SOLUTION: In a pressure change measuring device having a pressure sensitive part for detecting pressure change and a reference part for generating a reference signal for this pressure sensitive part, outside containers 51, 67 are provided in the pressure sensitive part and the reference part, and also a small hole 57 communicating with the outside is provided in the outside container 51 in the pressure sensitive part to transmit external pressure through this small hole 57, and in the outside container 67 in the reference part, an external medium is introduced relative to an inside container 52 to be sealed. Further, this device comprises the outside containers 51, 67 of a cylindrical shape and inside containers 52, 53 of a cylindrical shape which is coaxial with this outside container, and optical resonators 56, 63 are fitted on the inside containers 52, 53, and a deformation amount of the inside container is measured.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a pressure change measuring device which comprises a reference portion and a pressure-sensitive portion, and which is disposed on the seabed to measure a water pressure and to measure a tsunami.

[0002]

2. Description of the Related Art When a large earthquake occurs in a sea area, it is extremely important for disaster prevention to estimate the height of a tsunami in a coastal area within a very short time and to transmit the height to a related area. The tsunami warning system of the Japan Meteorological Agency predicts the wave height after an earthquake occurs based on empirical formulas based on the position and size. If the actual value of the sea level rise due to the tsunami is added to such a prediction system, the accuracy of the forecast will be significantly improved.

Conventionally, as a tsunami meter, there is a tsunami meter which is used, for example, by a cable type ocean bottom seismic constant observation system of the Japan Meteorological Agency. These are crystal vibration type water pressure change meters, which have sufficient resolution to detect pressure changes in tsunami measurement, but are susceptible to changes in the surrounding seawater temperature, and in reality, pure pressure There is a difficulty in detecting only the change. Further, a transport device or the like is required, and when used alone, it becomes expensive. Therefore, as an alternative to such conventional tsunami measurement means, the underground portion of a laser strain meter (Japanese Patent No. 2560260) already proposed by the present inventor is used as a water pressure gauge, and the optical fiber is used to reach the land. A tsunami wave height detection system that uses data transmission is conceivable. According to this system, a system with high accuracy, low price, and low maintenance cost can be realized. Hereinafter, a laser strain meter that the present inventor has already proposed will be described.

FIG. 4 is a diagram showing a configuration example of a laser strain gauge.
FIG. 5 is a diagram showing an example of a plane arrangement of the laser strain gauge. In the figure, 1 is a cylindrical container, 2 is a seal portion, 3 is an optical fiber, 4 and 9 are collimators, 5 and 10 are lenses, 6 and 1
1 is a right angle prism, 7 and 13 are concave mirror holders, 8 and 12
Indicates a concave mirror.

[0005] In FIG. 4, a cylindrical container 1 may be a corrosion-resistant pressure-resistant container made of metal, ceramic, or the like, and capable of measuring a small change in strain as a change in diameter. The inside of the cylindrical container 1 is evacuated in order to eliminate the influence of the temperature change of the medium, but when buried in the ground, the temperature is relatively stable, so that the container is filled with an inert gas. May be maintained.

The reference resonator is composed of a pair of concave mirrors 12, a collimator 9, a lens 10, and a right-angle prism 11, which are fixed at fixed intervals by a concave mirror holder 13 and are installed near the sensor resonator. From collimator 9
And a multiple reflection Fabry-Perot interferometer in which a laser beam is made to enter through the laser beam. On the other hand, the resonator for sensor uses the concave mirror holder 7 for the cylindrical container 1.
A plurality of concave mirrors 8, a collimator 4, a lens 5, and a right-angle prism 6, which are fixed to the inner wall of the optical fiber so that the diameter direction is the optical axis, so that a laser beam is incident from the optical fiber 3 through the collimator 4. Using a Fabry-Perot interferometer. Then, a plurality of sensor resonators are arranged such that the optical axes of the pair of concave mirrors 8 are different from each other.

FIG. 5 shows an example of the arrangement of concave mirrors constituting each resonator. The concave mirrors 8-1 and 8-1 ', 8-2 and 8-2', 8-3 and 8-3 'are shown. Can be arranged on the same plane by fixing the pair to the inner wall of the cylindrical container 1 so that their optical axes are oriented at 120 ° to each other. Also, by using a pair of concave mirrors 9 and 9 'as a reference resonator, and arranging them in the gap between the concave mirrors of the sensor resonator and fixing them at a constant interval, the mirrors can also be arranged on the same plane.

As the pair of concave mirrors 8 and 12, mirrors having particularly high reflectivity are used. For fixing the mirrors, maximum attention is paid to securing parallelism and matching optical axes. The concave mirror 8 and the right-angle prism 6 are firmly attached to the inner wall of the cylindrical container 1 by the concave mirror holder 7. In the reference resonator, a member having a small coefficient of thermal expansion is used for the concave mirror holder 13 and, of course, the concave mirror holder 13 is arranged so that the deformation of the cylindrical container 1 does not affect the distance between the pair of concave mirrors 12.

In this laser strain gauge, light from a laser oscillator on the ground is guided from the outside of the cylindrical container 1 through the seal portion 2 to the inside by the optical fiber 3. Then, the light beams collimated by the collimators 4 and 9 are focused into the resonator (cavity) by the lenses 5 and 10 and are reflected by the prisms 6 and 11 to be reflected from the concave mirrors 8 and 12 into the resonator. Make it incident. The light guided into the resonator resonates at a frequency corresponding to the distance between the concave mirrors 8 and 12.

FIG. 6 is a diagram showing a configuration example of a signal processing system on the ground side of a laser strain meter, wherein 21, 24, and 30 are couplers, 22, 28, 31, and 32 are isolators, and 23 and 3 are shown.
4 is a laser oscillator, 25 is a high-speed photodetector, 26 is a counter, 27 and 35 are feedback circuits, 29 and 3
Reference numeral 3 denotes a low-speed photodetector.

As shown in FIG. 4, a pair of optical fibers 3 are guided to each resonator, and are optically connected one by one to two concave mirrors 8 and 12 forming a pair of each resonator. The laser light from the external laser oscillators 23 and 34 as shown in FIG. 6 is guided to one optical fiber 3, and the light in the resonator is fed to the feedback circuits 27 and 35 through the other optical fiber 3. Be guided. The isolators 22 and 31 are
The reverse light from the underground resonator is again emitted by the laser oscillator 2
The isolators 28 and 32 prevent reflected light from the low-speed photodetectors 29 and 33 from entering the underground resonator.
The feedback circuits 27 and 35 expand and contract the piezo elements of the laser oscillators 23 and 34 so that the resonance frequencies of the laser oscillators 23 and 34 match the resonance frequency of the resonators. Is controlling.

The laser oscillator 2 controlled as described above
The laser light guided into the resonator from 3 and 34 is taken in from the couplers 21 and 30 for measurement. Then, the coupler 24 adds the light of the sensor resonator taken in through the coupler 30 and the light of the reference type resonator taken in through the coupler 21 to the photodetector 25, and causes the photodetector 25 to operate. The difference between the resonance frequencies of the device and the reference type resonator is detected by the counter 26. Therefore, three resonance frequency differences are obtained,
When these are used, a strain change is obtained as follows.

The difference between the three resonance frequencies is represented by Δω ₁ , Δω ₂ ,
If Δω ₃

[0014]

Δω ₁ = ω ₁ −ω _ref Δω ₂ = ω ₂ −ω _ref Δω ₃ = ω ₃ −ω _ref where ω ₁ , ω ₂ , ω ₃ and ω _ref are three sensor resonators and The resonance frequency of the reference resonator, ω ₁
Given that ≒ ω ₂ ≒ ω ₃ ≒ ω _ref

[0015]

## EQU2 ## Δω ₁ / ω ₁ = Δω ₁ / ω _ref = −Δd ₁ / d
→ Δd ₁ = − (Δω ₁ / ω _ref ) d Here, Δd ₁ is the amount of expansion and contraction of the diameter in the sensor direction. Likewise

[0016]

## EQU3 ## Δd ₂ = − (Δω ₂ / ω _ref ) d Δd ₃ = − (Δω ₃ / ω _ref ) d In this manner, three independent diameter variations can be obtained. The three components of strain change can be determined based on the theory of strain measurement due to change.

[0017]

FIG. 7 is a diagram showing an example of using a laser strain gauge for a tsunami meter. Usually offshore 100
Since it takes about 10 to 20 minutes for the tsunami to reach the coast from km, as shown in FIG. 7, the underground part of the laser strain gauge is laid as a laser water pressure gauge 41 on the sea floor 100 km offshore, for example. By connecting the optical fiber submarine cable 42 between the laser device 41 and the ground-based laser device 43, the tsunami meter can be used as a tsunami meter that can predict 10 to 20 minutes before arrival.

However, in the case of the above laser strain meter, if the minute strain change of the crust buried in the ground is measured as a change in diameter, there is no problem because the temperature in the borehole is very stable. However, if this is used as it is as a tsunami meter, it will be affected by changes in water temperature due to sea bottom water currents and the like, causing a problem.

That is, when the above laser strain gauge is installed on the sea floor as a tsunami meter, if the temperature environment changes suddenly due to the sea bottom water flow or the like, the deformation due to the thermal expansion or contraction of the cylindrical container due to the temperature change is caused by the water level change. To the same degree as deformation due to Further, even if there is a change in the water temperature, there is no problem if both the temperature change of the sensor resonator and the temperature change of the reference resonator are synchronized.

[0020]

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problems, and it is an object of the present invention to eliminate an influence caused by a sudden change in a temperature environment caused by an external flowing medium such as a seabed water stream.

For this purpose, the present invention relates to a pressure change measuring apparatus having a pressure-sensitive portion for detecting a pressure change and a reference portion for generating a reference signal for the pressure-sensitive portion. A container is provided, and a small hole communicating with the outside is provided in the outer container in the pressure-sensitive portion, and external pressure is transmitted through the small hole. Is introduced and enclosed. Further, the present invention is characterized by comprising a cylindrical outer container and a cylindrical inner container coaxial with the outer container, wherein an optical resonator is attached to the inner container and the amount of deformation of the inner container is measured.

[0022]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a view showing an embodiment of a pressure change measuring device according to the present invention, in which 51 and 67 are outer cylindrical containers, 52 and 53 are inner cylindrical containers, 54 is an inner lid,
5 is an optical fiber, 56 is a sensor resonator, 57 is a pressure transmission small hole, 58 is an external communication part, 61 is a cable connection part,
62 is a seal portion, 63 is a reference resonator, 64 is a sealed portion,
Reference numeral 65 denotes a small hole for encapsulation, and 66 denotes a plug for encapsulation.

In FIG. 1, a pressure change measuring device according to the present invention comprises a connecting portion, a pressure-sensitive portion for detecting a pressure change across the connecting portion, and a reference portion for generating a reference signal for the pressure-sensitive portion. And the pressure-sensitive part and the reference part are the outer cylindrical containers 51, 67
And inner cylindrical containers 52 and 53, respectively. The inner cylindrical containers 52 and 53 are fixed to the outer cylindrical containers 51 and 67, respectively, with the connection side closed by the inner lid 54,
Outer cylindrical containers 51, 6 around inner cylindrical containers 52, 53
7, an external communication portion 58 or a sealing portion 64 is provided. The external communication part 58 is connected to the outer cylindrical container 5 in the pressure sensing part.
At least one pressure transmitting small hole 57 is provided in 1 to form a space communicating with the outside of the outer cylindrical container 51, and a sensor resonator 56 having a reflecting mirror, a prism, and a collimator is provided in the inner cylindrical container 52. Provided. The sealing portion 64
At least one small hole 65 for sealing is provided in the outer cylindrical container 67 in the reference portion, and an external medium (seawater, gas, etc.) is introduced and sealed with the sealing plug 66 to shut off the outside of the outer cylindrical container 67. A reference resonator 63 having a reflecting mirror, a prism, and a collimator is provided in the inner cylindrical container 53.

Optical fiber 55 externally connected to the sensor resonator 56 of the pressure sensitive section and the reference resonator 63 of the reference section.
Is guided to the connecting portion through the sealing portion 62 of the inner lid 54 of the inner cylindrical containers 52 and 53, and is drawn out of the connecting portion through the cable connecting portion 61 to the outside. In addition, an inert gas, for example, is sealed in the inner cylindrical container 52 of the connecting portion and the pressure-sensitive portion and in the inner cylindrical container 53 of the reference portion.

Next, a description will be given of a case where the pressure change measuring device according to the present invention configured as described above is used, for example, as a tsunami meter by being settled on the sea floor. First, at the time of installation, the sealing plug 66 of the reference portion is removed and seawater is introduced into the sealing portion 64 from the sealing hole 65, and then the sealing hole 65 is closed with the sealing plug 66, so that the seawater is filled in the sealing portion 64. Is enclosed.
When the tsunami meter is submerged on the sea floor, most of the pressure change from the outside at the reference part is received by the outer container, and the pressure change outside the inner container is very small. As a result, the inner container 53 of the reference portion is hardly affected by the pressure change applied to the outside of the outer cylindrical container 67, or is very small at all. On the other hand, the inner cylindrical container 52 in the pressure-sensitive portion
The outside of the outer cylindrical container 51 is formed by a pressure transmitting small hole 57.
Since the cylinder is deformed in response to an external pressure change, the diameter change at this time can be detected by the sensor resonator 56 because the external communication portion 58 is filled with seawater in communication with the outside. it can.

Although the seawater between the inner and outer cylinders of the pressure-sensitive part communicates with the outside through small holes, the exchange of the inner and outer seawater is very small due to the small diameter of the holes. Also, the thermal conductivity of water in the pores is much lower than that of metal. Also, the pressure-sensitive part,
Considering that seawater in contact with the inner cylinder of the pressure-sensitive part and seawater sealed between the inner and outer cylinders of the reference part are almost the same in terms of physical properties, the inner part due to external temperature fluctuations It is considered that the time change of expansion or contraction due to the temperature of the cylinder is almost the same in the reference portion and the pressure-sensitive portion.

To summarize the above, external pressure fluctuations affect the inner cylinder of the pressure sensing portion, but do not affect the inner cylinder of the reference portion. On the other hand, the external temperature change equally affects both cylindrical portions. With this mechanism, the difference between the diameter change of the inner wall of the inner cylinder of the pressure sensing unit and the change of the diameter of the inner wall of the inner cylinder of the reference unit is changed by the pure pressure change which is not affected by the temperature.

The above can be expressed by the following equations. The internal diameter of the inner cylinder of the pressure-sensitive part and the reference part in a certain reference state is D. At some point, it is assumed that the temperature and pressure of the external seawater change stepwise by ΔT and ΔP. At this time, assuming that the inner diameters of the inner cylinders of the pressure-sensitive portion and the reference portion are Ds and Dr,

[0029]

Ds = D (1 + As (t) ΔT) (1-BsΔP) Dr = D (1 + Ar (t) ΔT) (1-BrΔP)

Here, As (t) and Ar (t) are coefficients (functions of time) indicating how the pressure-sensitive part and the reference part inner cylinder expand transiently due to temperature change. Specifically, it is the same as the coefficient of linear thermal expansion of the material constituting the cylinder. Although the pressure-sensitive portion outer cylinder has small holes as described above, it does not significantly affect how heat is transmitted from outside to inside. Therefore,

[0031]

## EQU5 ## It may be considered that As (t) = Ar (t) = A (t).

Bs and Br are coefficients indicating how the inner cylinder contracts due to pressure. As described above, Br is very small or close to zero.

[0033]

## EQU6 ## Bs≫Br. By putting the relationship of Equation [Equation 5] into Equation [Equation 4], the difference between the inner diameters of the inner cylinders of the pressure-sensitive part and the reference part becomes:

[0034]

Ds−Dr = −D (1 + A (t) ΔT) (Bs
−Br) ΔP. The maximum value of A (t) is the coefficient of linear thermal expansion α (≒ 1
0 ⁻⁵ ), and considering that it is much smaller than 1, when [Equation 6] is put into [Equation 7],

[0035]

Ds−Dr = −BsΔP Here, Bs can be determined based on a calculation or a test based on a change in pressure. Thus, the actual observation (Ds
By obtaining −Dr), ΔP free from the influence of temperature can be known.

FIG. 2 is a diagram showing another embodiment of the pressure change measuring device according to the present invention, and FIG. 3 is a diagram showing a modified example of the pressure change measuring device according to the present invention. Containers, 72 and 73 are inner cylindrical containers, 74 is an inner lid, 75 is an outer lid, 76 is a resonator for sensor, 77 is a small hole for pressure transmission,
78 is an external communication part, 79 and 87 are gas filled parts, 80 is an optical fiber, 81 is a cable connection part, 82 is a seal part, 8
3 is a reference resonator, 84 is a sealing portion, 85 is a small hole for sealing,
Reference numeral 86 denotes a sealing plug.

In this embodiment, a cable connecting portion 81 for drawing an optical fiber is provided not on the intermediate connecting portion but on the side opposite to the connecting portion of the reference portion. The inner cylindrical container 73 of the reference portion and the space of the connecting portion are integrated, and for example, an inert gas is sealed therein. Similarly, an inner lid 74 is provided on the side opposite to the connection between the inner cylindrical containers 72 and 73, and the outer cylindrical container 7
An outer lid 75 is provided on the side opposite to the connecting portion of each of the first and the 88, and a gas sealing portion 79, 87 is provided between the inner lid 74 and the outer lid 75.
And Then, by fixing the inner cylindrical containers 72 and 73 to the outer cylindrical containers 71 and 88 at both ends, an external communication portion 78 or a sealing portion 84 is formed between the outer periphery thereof and the outer cylindrical containers 71 and 88. ing.

As described above, in the pressure change measuring device according to the present invention, the pressure sensing portion and the reference portion have a double cylindrical structure including the outer cylindrical container and the inner cylindrical container, and the gap space between the outer cylindrical container and the inner cylindrical container is defined. , The pressure-sensitive part communicates with the outside through a hole,
The reference portion is sealed so as to eliminate the influence of a sudden change in the temperature environment outside the outer cylindrical container. Therefore, in addition to the configuration shown in FIG. 1 and FIG. 2, the pressure-sensitive portion, the connection portion, and the reference portion are not linear, but the pressure-sensitive portion and the connection portion are arranged side by side with respect to the connection portion as shown in FIG. Various configurations can be adopted for the arrangement configuration.

It should be noted that the present invention is not limited to the above embodiment, and various modifications are possible. For example, in the above-described embodiment, an example in which two pressure transmitting small holes and two sealing small holes are provided has been described. However, even one pressure transmitting or sealing is possible, and conversely, three or more holes may be provided. Needless to say. In addition, the case of immersion on the seabed and used as a tsunami meter has been described. However, it may be used as a tide gauge or other water level gauges, or gas pressure and vacuum It may be used for other measurements. Further, the container is not limited to a cylindrical container, but may be applied to a container of another shape as long as it is a double container, and the example using a laser strain gauge has been described, but a differential transformer or a digital displacement sensor is used. Alternatively, the present invention may be similarly applied to a device for measuring a change in diameter due to a pressure change using, for example, or a device for measuring a change in volume using a differential transformer by enlarging the movement of a bellows.

[0040]

As is apparent from the above description, according to the present invention, the outer container is provided in the pressure-sensitive portion and the reference portion, and the outer container in the pressure-sensitive portion has at least one or more communicating with the outside. A plurality of small holes are provided to transmit external pressure through the small holes, and one or a plurality of small holes are provided in the outer container in the reference portion to introduce an external atmosphere and to be sealed with a plug. Pressure changes the inner container of the pressure sensitive part, but does not substantially affect the inner container of the reference part. On the other hand, external temperature changes have a similar effect on the pressure sensitive part and the inner container of the reference part. Therefore,
The difference between the change in the inner diameter of the inner container of the pressure-sensitive portion and the change in the inner diameter of the inner container of the reference portion can be detected as being solely due to the pressure change without being affected by the temperature.

[Brief description of the drawings]

FIG. 1 is a diagram showing an embodiment of a pressure change measuring device according to the present invention.

FIG. 2 is a diagram showing another embodiment of the pressure change measuring device according to the present invention.

FIG. 3 is a diagram showing a modified example of the pressure change measuring device according to the present invention.

FIG. 4 is a diagram illustrating a configuration example of a laser strain meter.

FIG. 5 is a diagram showing an example of a planar arrangement of a laser strain gauge.

FIG. 6 is a diagram illustrating a configuration example of a ground-side signal processing system of the laser strain meter.

FIG. 7 is a diagram showing an example of using a laser strain meter for a tsunami meter.

[Explanation of symbols]

51, 67: outer cylindrical container, 52, 53: inner cylindrical container, 54: inner lid, 55: optical fiber, 56: resonator for sensor, 57: small hole for pressure transmission, 58: external communication part, 61
... Cable connection part, 62 ... Seal part, 63 ... Reference resonator, 64 ... Enclosure part, 65 ... Small hole for encapsulation, 66 ... Sealing stopper

Claims (3)

[Claims] 1. A pressure change measuring device having a pressure-sensitive part for detecting a pressure change and a reference part for generating a reference signal for the pressure-sensitive part, wherein an outer container is provided for the pressure-sensitive part and the reference part. In the outer container of the pressure-sensitive part, a small hole communicating with the outside is provided to transmit external pressure through the small hole, and the outer container in the reference part introduces an external medium between the outer container and the inner container. A pressure change measuring device characterized by being configured to be enclosed. 2. The pressure change measuring device according to claim 1, comprising a cylindrical outer container and a cylindrical inner container coaxial with the outer container. 3. The pressure change measuring device according to claim 1, wherein an optical resonator is attached to the inner container to measure an amount of deformation of the inner container.